The present invention relates generally to ironing machines or bodymakers and more specifically to an improved drawing and ironing apparatus for use with a punch that reforms the cup and then reduces the sidewall thereof.
In the formation of a "two-piece" container, it has been customary to utilize a plurality of die assemblies that cooperate with a punch for converting circular metal discs into finished containers. Usually this is accomplished in two steps. A circular metal disc is originally drawn into a cup utilizing what is commonly referred to as a cupping machine. The cup is then transferred to a bodymaker or press wherein the cup is converted into the finished container. One type of commercial machine that is presently available is produced by Ragsdale Bros., Inc. and is identified as a Model CR-24 can wall drawing and ironing press.
The press or bodymaker of this type includes a cup redraw assembly, a plurality of ironing assemblies and a stripper assembly arranged seriatim along a path for a punch. The cups for this machine are originally larger in diameter than the finished internal diameter of the container and the cup is initially redrawn by the redraw assembly and the sidewall thereof is then reduced in thickness by cooperation between the punch and the plurality of ironing assemblies. At the end of the stroke for the punch, the end wall of the container is reformed generally to a dome shaped configuration.
In order to produce conventional 12 and 16 ounce containers, the length of the stroke of the punch for the press or bodymaker must be fairly long and has heretofore created substantial problems in producing a satisfactory container which has a uniform wall thickness in the sidewall thereof. One of the problems encountered has been in maintaining all of the elements in very accurate alignment with respect to each other in order to produce a finished container that has a uniform wall thickness around the entire perimeter thereof and also along the entire length thereof.
In order to alleviate some of the problems in maintaining accurate alignment between the various die assemblies and the punch, it has previously been proposed to utilize floating ironing die assemblies so that the ironing die can move radially of the path of the punch in order to obtain a more uniform sidewall thickness for the finished container. For example, British Pat. No. 724,251, published Feb. 16, 1955, discloses a method of supporting ironing dies that will accommodate movement of the dies with respect to the punch but will also provide a self-centering feature which theoretically will reposition the die to a predetermined position whenever external forces have been removed. The particular arrangement for accomplishing the self-centering and floating feature in the assembly disclosed in the British patent consists of cooperating inclined surfaces between the ironing die and its support mechanism with a biasing mechanism which will also center the ironing dies with respect to a predetermined axis whenever external forces are removed. The biasing mechanism in this patent has been illustrated as either consisting of an elastomeric member or rubber ring which produces a centering action between the ironing die and the cooperating support or springs that cooperate with the ironing die and the support to center the die with respect to a predetermined axis.
Other types of centering means have been utilized in conjunction with the ironing assemblies. Another example consists of an ironing die support which supports an ironing ring with a centering ring surrounding the ironing ring. The centering ring has spring biased plungers biased into engagement with the periphery of the support to accommodate radial movement of the support with respect to the predetermined path.
The centering mechanisms consisting of radially biased plungers have been used successfully in overcoming problems in obtaining uniform wall thickness for the container. However, one additional problem has been encountered in the reforming of the cup in a redrawing process. Heretofore, it has been deemed necessary to have the redraw ring which cooperates with the punch in a fixed position which defines the centered position for the punch during its stroke in producing a drawn and ironed container.
In redrawing a cup to its reduced diameter it is customary to utilize a sleeve that cooperates with the redraw ring and is initially inserted into the cup and forces the cup against the top surface of the redraw ring. Thereafter, the punch is passed through the sleeve and forces the cup through the redraw ring. Thus, if there is any misalignment between the sleeve and the redraw ring, the cup will be redrawn unevenly which may result in an unsatisfactory cup since there may not be sufficient metal around certain peripheral portions of the sidewall in order to produce a container of a particular height.
In one type of redraw assembly, a nesting ring surrounds the opening in the redraw ring and has an opening which conforms to the original size of the cup. The nesting ring is fixed with respect to the redraw ring and acts as a pilot for generally centering the cup with respect to the redraw ring.
A further problem that has been encountered is the inability of supplying lubricants in an accurate controlled flow between the surface of the redraw ring and the adjacent surface of the cup in the most critical area which is the area above or on the upper surface of the redraw ring.
A further problem encountered with drawing and ironing assemblies of the above type relates to the stripper assembly. If the ironing rings are mounted in a floating fashion, the ironing rings will assume a centered position with respect to the axis of the punch as the punch passes therethrough. This will result in a fairly uniform wall thickness of the container. However, should the axis of the punch be offset to some degree with respect to a predetermined path, the stripper assembly may cause damage to the outer surface of the container, such as producing scratches therein which will make the container unsatisfactory for use. Also, if the stripper assembly in not exactly aligned with the axis of the punch, the stripper jaws may apply unequal forces to the free edge of the container and deform the edge and rim of the container. In certain cases of mislaignment, some of the stripper jaws may not engage the edge of the container.